The water cycle and water insecurity

  • Created by: sophie000
  • Created on: 11-12-17 19:05

The Drainage Basin

The Drainage Basin is a subsystem within the global hydrological cycle. It is an open system with inputs and outputs that cause the amount of water in the basin to vary over time.  The boundary of the drainable basin is defined by the watershed

Physical Factors affecting The Drainage Basin:

  • Precipitation
  • Interception
  • Direct runoff
  • Evaporation and transpiration

Human Factors affecting The Drainage Basin:

  • Farming and irrigation
  • Deforestation
  • Construction of dams
  • Overpopulation
  • Global warming
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The Drainage Basin (more detail)

Physcial Factors affecting Drainage Basins

  • Precipitation = Varies according to type and intensity over time and space, linked to climate and weather systems
  • Interception = Where water is prevented from reaching the ground by vegetation. The rate is dependent on precipitaion and vegetation
  • Direct run off = Rainfall running off the surface. Any surface runoff will deliver water into river channels increasing the risk of flodding downstream
  • Evaporation and Transpiration = Affected by temperature, vegetation cover and soil moisture content
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Water Budgets

Water Budget is the annual balance between inputs (precipitation) and outputs (evaporation)


Precipitation = Channel discharge + evapotranspiration +/- change in storage

  • They can be used to monitor the amount of water held in stores
  • Influenced by the type of climate
  • Great importance to farmers
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River Regimes

A river regime is an annual variation of the discharge or flow of a river.

It is particularly affected by climate, geology and soils.


1. Amazon River (South America) - humid tropical climate, regime linked to snow melt from the Andes

2. River Nile (Northern Africa) - warm arid climate, huge drainage basin, the construction of the Aswan Dam altered the regime of the river

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Definition - An extended period of a deficient rainfall relative to the statistical multi - year average for a region

Examples -

Meteorological Drought - this happens where long term precipitation is lower than normal and is affected by the atmospheric conditions

Agricultural Drought - this happens where there is not enough soil moisture to allow crops to grow. Caused by precipitation shortages and reduced groundwater levels

Hydrological Drought - this happens when the amount of surface and subsurface water is deficient. Caused by lack of precipitation

Socio economic Drought - occurs when water deman outstrips the water availability

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El Niño - Southern Oscillation

ENSO is a large mass of warm air in the Pacific Ocean

It occurs regularly but not predictably (every 2-7 years)

El Niño events are reversal of the normal directions of ocean currents and winds in the Pacific Basin.

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How do human activities increase the risk of droug

  • Overabstraction of groundwater - Coca Cola in Kerala didn't cause a drought but there wasn't enough water left for everyday needs and agriculture
  • Construction of dams and reserviours and water transfer projects - North south transfer project and the Three Gorges Dam in China have attempted to change the country's water balance
  • Changing land use and deforestation - less vegetation means that less evapotranspiration can occur, so less atmospheric moisture. Also, soil becomes compacted which reduces infiltration
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The impact of drought on ecosystems

Wetlands - an area, which is either permanently or seasonally saturated with water

  • Areas of water dry up or shrink which can cause habitats to be damaged or lost
  • Soil moisture drops causing soil erosion to occur as more land is exposed
  • Food webs can change as certain species are more or less resilient to drought

Forests -

  • Trees can take 2-4 years to recover from drought but some species are less resilient
  • Trees do not grow properly and can be more susceptible to pests and diseases

RAMSAR - The RAMSAR Convection on Wetlands protects 1.7 milliom k2 of wetland

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Meteorological causes of flooding

  • Much flooding in the UK is the result of mid latitide depressions forming from low air pressure
  • These usually bring showers and rain
  • When rain is prolonged the ground becomes saturdated. When this happens the precipitaion is transferred as runoff, moving it quickly to river channels and increasing the river flow
  • Once the channel is exceeded, water will break the banks and flow into the floodplain
  • This happens when the jet stream is hovering around the mid-latitudes
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  • These occur very quickly and without warning
  • These usually happen when there has been intense, heavy rainfall
  • Usually not much inflitration happens, therefore run off is rapid and there is a very short lag time

Example -

In 2004, Roscastle in Cornwall experienced a 1 in 400 year flood, after 8 hours of intensive rainfall. 75 cars were washed away and 100 homes lost. £15 million of damage

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  • Caused by seasonal change in the direction of prevailing winds
  • Warm moist air from the Indian Ocean blows towards the Indian subcontinent
  • This brings a humid climate and torrential rain
  • Happens because the ITCZ moves northwards, driving the low pressure further north and brining in the rain
  • Around 70% of average rainfall occurs in just 100 days
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  • In high latitudes and mountain areas, snowmelt can add to the river capacity.
  • Melting snow in the late spring affects Asia and America
  • Rapid melting occurs but due to lower regions remaining frozen, there is not a high rate of inflitration - can sometimes be held up by dams
  • Glacial outbursts can also occur in places like the Himalayas and Iceland which releases meltwater, called Jokulhaups
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Physical factors affecting flooding levels

1. Vegetation  - produces higher levels of interception, storage and evapotranspiration

2. Slope - greater the slope means more run off

3. Rock type - allows greater infiltration and ground storage

4. Drainage density - reduced risk of flooding if low

5. Soil depth - absorbs more water and less runoff

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Socio - economic impacts of flooding

1. The impact of river depth and velocity suggests that water 0.5m deep can wash cars away, and the foundation of buildings start to collapse

2. Flood depth in developing countries is a threat because people have not learnt to swim and be killed by poisonios snakes

3. Flood can affect people's livelihoods. There is many structural damage to property and many people get concerned about getting flood insurance and coping with reduced property values

4. Crops, livestock and agricultural infrastructure suffer major damage. At subsistence farming, there is direct loss of food supplies and risk of famine. In developed countries, food prices can rise

5. EXAMPLE - In Cumbria, flooded electricty stations meant that people were without power for 3 days

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Environmental impacts of flooding

1. In natural ecosystems, floods help to maintain key ecosystem functions and biodiversity

2. Floods can recharge groundwater systems, fill wetlands, increase connectivity between aquatic habitats and move sediment and nutrients around the landscape

3. Environments degraded by human activities are more affected

4. EXAMPLE - When the Aswain Dam was built in the Nile Basin, one of the aims was to control flooding in the Nile. This had a negative impact on subsistence farmers and also on Sardine fishermen

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Climate change impacting the hydrological cycle

1. Increased GHG emissions from human activity

2. More heat trapped leading to enhanced GHE

3. Increase in average air and ocean surface temperature

4. Decreased snow, permafrost and ice cover. Increased in meltwater will increase river flooding in the immediate future but then decrease afterwards

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Water insecurity


Water insecurity exists when population no longer has sustainable access to adequate quantities of water of acceptible quality. Adequate in sustaining human well-being and socio-economic development and for ensuring protection against water-borne pollution and disease.


According to the UN, water use has grown twice as fast as population growth in the last century

Two thirds of the world's population could be living under water stress conditions

By 2025, 1.8 billion people will be living in places with absolute water security

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Physical and human causes of water insecurity


  • Climate - this determines the global distribution of water supply via precipitation, but precipitation varies not only from place to place but also seasonally.
  • Salt water encroachment - rising sea lvels and coastal erosion leading ot he contamination of freshwater by seawater in coastal areas
  • Over abstraction of water rrom rivers, lakes and groundwater
  • Pollution of water stores and flows resulting from agricultura; amd industrial effluents


  • Population growth
  • Rising living standards
  • Industrialisation
  • Commercial agriculture
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Why is water important?


  • Water supply needs to be reliable to help economic growth
  • Energy production demands a lot of water and so our increasing demand for energy will put more stress on freshwater
  • Water is needed got producing goods and services


  • A lack of investment in basic water infrastructure means that children in the developing world still suffer and die daily.
  • Poverty links with a lack of access to clean water and the health of people in developing nations
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Different approaches to managing water supply

Hard engineering

This is a 'technological fix' to manage water. It includes approaches such as dams, water transer projects amd desalinisation (conversion of salt water into fresh water)


This is using methods that are more natural. It includes effective water management, recycling, conservation and restoring aquifers

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Key players in managing water supply


  • United Nations
  • Governments
  • European Union
  • Major NGOs e.g. WaterAid


  • Planners
  • Environmentalists
  • Water companies
  • Water users
  • Local governments
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